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Achieving Convergence-Free Routing using Failure-Carrying Packets

Achieving Convergence-Free Routing using Failure-Carrying Packets. K. Lakshminarayanan et al. Presented by Ang Li 06/29/07. Convergence is the source of evil!. Packet Loss LSA storms (high control message overhead) High CPU utilization Network instability What we have

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Achieving Convergence-Free Routing using Failure-Carrying Packets

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  1. Achieving Convergence-Free Routing using Failure-Carrying Packets K. Lakshminarayanan et al. Presented by Ang Li 06/29/07

  2. Convergence is the source of evil! • Packet Loss • LSA storms (high control message overhead) • High CPU utilization • Network instability • What we have • Loop-free convergence • Fast convergence • Backup paths

  3. FCP, no convergence at all! • No control message exchange • Routes calculated “on-demand” • When a packet meets a failure • Packets carry topology information • Failure list • To avoid loop

  4. FCP algorithm

  5. Why FCP works? • A stable and consistent Network Map • FCP falls back to normal link-state protocol when no failure • Guarantee efficiency • Failure list grows monotonically • Guarantee loop-free

  6. FCP with Source Routing • To deal with inconsistent Network Map • FCP packets carry the whole path besides failure list • Differences in Network Map are reported as “failures” • Higher packet overhead

  7. Two Properties of FCP • Guaranteed Reachability • Packets are delivered within finite time if the network is still connected • Time is bounded by number of failures and network diameter • Path Isolation • Routers not on the forwarding path of one packet can not affect the forwarding

  8. Reducing Overhead of FCP • Two overheads • Computation time • Packet overhead

  9. Reducing Overhead of FCP • Two overheads • Computation time • Solution: precompute “secondary nexthop” & caching • Packet overhead • Solution: mapping between failure list and label

  10. Network Map Dissemination • Centralized scheme • Need special care to guarantee consistency • Otherwise FCP-SR is used

  11. Pros of FCP • Theoretically interesting • A new approach • Provide two layers of topology update • Network Map layer • Failure layer • Security • Influence of a hijacked router is limited

  12. Cons of FCP • Far from practical deployment • Many details missing • For e.g., how to do caching? How much caching is enough? • Inconsistent with today’s router architecture • Route computation can not be carried out in linecards • Idea is not new • Already in wireless context • The only thing new is the concept of Network Map

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